1. Field of the Invention
The present invention relates to an improvement in a lens barrel, and more specifically, to an improvement in a retaining structure of a moving frame which moves in a direction of an optical axis while being guided by a guide frame.
2. Description of the Prior Art
Most conventional movable lens frames and moving frames such as helicoid rings in lens barrels are designed so that the outer periphery thereof is loosely fitted with the inner surface of a fixed cylinder as a guide frame or a helicoid ring or the like, or threadably engaged with the helicoid ring to retain a position with respect to the optical axis. In such a retaining construction of diametral fitting, the precision of loose fitting or threaded engagement must be increased in order to effect displacement of the moving frame in a direction of an optical axis smoothly without play, and thus such a construction poses disadvantages in that machining costs are expensive. It is also necessary to coat a lubricating agent on the sliding frictional surface because of a large sliding frictional area with the result that the interior of the barrel tends to be contaminated. Further, the sliding frictional surface is exposed alongside the optical axis and as a result, internal reflection tends to occur. In television cameras and cinecameras, it is known that a guide frame and a moving frame engage a rail at an engaging portion in contact therewith to retain a position of the moving frame with respect to the optical axis. Such a retaining construction may obtain the effect in which the sliding frictional area is decreased to reduce a moving resistance of the moving frame but will not overcome a problem in which the sliding frictional surface is exposed even though the area is decreased.
On the other hand, a guide construction of a moving frame is known from Japanese Patent Publication No. 27560/1964 wherein a fixed frame and a moving frame are shaped to have of multiple of guide tongues in the form of a streamer, the guide tongues being engaged with each other so that the moving frame may be guided in a direction of the optical axis. Such streamer-like cantilever guide tongues are likely to produce deformation, posing a problem in practical use. That is, the cantilever guide tongues are relatively stable in a circumferential direction where they engage each other but tend to produce deformation in a radial direction, which is extremely difficult to work out.